Research is being conducted on the mechanism(s) involved in the induction of oocyte maturation (amphibian) with steroid hormones. Two general approaches are being undertaken. The first concerns the hypothesis that the initial site of steroid action is at the membrane level, resulting in the release of bound calcium. This in turn, through mediation by the calcium binding protein calmodulin, activates a series of enzymatic steps leading to germinal vesicle breakdown. Changes in calcium ion concentration are monitored with the photoprotein aequorin. The role of calmodulin, isolated and purified from frog oocytes, is being monitored by isolation of calmodulin-binding proteins on affinity columns coupled with an assay in vitro and in vivo of enzymatic activities. The second general approach covering the nature and control of changes in protein synthesis known to occur in maturing oocytes. The major technique has involved microinjecting specific exogenous mRNAs into oocytes, followed by assays of the degree of competition for endogenous mRNAs for translation. In this way, we hope to monitor the role of specific components (such as initiation factors) as rate limiting factors before and during the steroid-induced period of oocyte maturation.